МИКРОБНАЯ БИОРЕМЕДИАЦИЯ ПОЧВ, ЗАГРЯЗНЕННЫХ УГЛЕМ И ПОЛИЦИКЛИЧЕСКИМИ АРОМАТИЧЕСКИМИ УГЛЕВОДОРОДАМИ: МЕХАНИЗМЫ ДЕГРАДАЦИИ И СОВРЕМЕННЫЕ ПОДХОДЫ: КРАТКИЙ ОБЗОР

УДК 628.3+576.5

Abstract

Soil contamination by coal and its processing by-products, including polycyclic aromatic hydrocarbons (PAHs) and their derivatives, represents a significant environmental problem due to their high persistence, toxicity, and bioaccumulation potential. This review summarizes current knowledge on the composition of coal-related pollutants, their environmental risks, and the limitations of conventional physicochemical remediation methods. Particular attention is given to the role of microorganisms in bioremediation processes, including bacteria, fungi, and microbial consortia capable of effective transformation and mineralization of hydrocarbons.

The mechanisms of microbial degradation of PAHs are discussed, including enzymatic pathways involved in the oxidation and cleavage of aromatic structures, as well as key factors influencing bioremediation efficiency (temperature, pH, aeration, bioavailability, and nutrient availability). It is shown that optimization of environmental conditions, along with the application of biostimulation and bioaugmentation strategies, significantly enhances the remediation of contaminated soils. The перспективность of synthetic microbial consortia and advanced biotechnological approaches for improving the degradation of complex pollutants is also highlighted.

Аннотация

Загрязнение почвы углем и продуктами его переработки, включая полициклические ароматические углеводороды (ПАУ) и их производные, представляет собой серьезную экологическую проблему из-за их высокой стойкости, токсичности и потенциала биоаккумуляции. В данном обзоре обобщены современные знания о составе загрязняющих веществ, связанных с углем, их экологических рисках и ограничениях традиционных физико-химических методов ремедиации. Особое внимание уделяется роли микроорганизмов в процессах биоремедиации, включая бактерии, грибы и микробные консорциумы, способные эффективно преобразовывать и минерализовать углеводороды.

Обсуждаются механизмы микробной деградации ПАУ, включая ферментативные пути, участвующие в окислении и расщеплении ароматических структур, а также ключевые факторы, влияющие на эффективность биоремедиации (температура, pH, аэрация, биодоступность и доступность питательных веществ). Показано, что оптимизация условий окружающей среды, наряду с применением стратегий биостимуляции и биоусиления, значительно повышает эффективность ремедиации загрязненных почв. Также освещается перспективность синтетических микробных консорциумов и передовых биотехнологических подходов к улучшению разложения сложных загрязняющих веществ.

Keywords: soil pollution, bioremediation, coal contamination, polycyclic aromatic hydrocarbons (PAHs), microbial degradation, microbial consortia

Ключевые слова: загрязнение почвы, биоремедиация, загрязнение углем, полициклические ароматические углеводороды (ПАУ), микробная деградация, микробные консорциумы

1. Introduction

Soil contamination by coal and its processing by-products represents a serious environmental issue, particularly in industrialized regions. During coal mining, transportation, and combustion, a wide range of toxic compounds is released into the environment, including polycyclic aromatic hydrocarbons (PAHs), resins, and other organic pollutants [32]. These compounds are characterized by high persistence, toxicity, and carcinogenicity, making them hazardous to ecosystems and human health.

PAHs are organic compounds composed of two or more fused aromatic rings and are widely distributed in soils of industrially contaminated areas. Their main sources include pyrogenic processes (incomplete combustion of organic fuels) and petrogenic inputs associated with petroleum and coal [15, 33]. Due to their high chemical stability, hydrophobicity, and bioaccumulation potential, PAHs persist in soils for long periods and exert long-term adverse effects on living organisms.

A further challenge is the limited range of compounds considered in most studies. Typically, environmental assessments focus on the 16 priority PAHs defined by the US Environmental Protection Agency (US EPA), whereas alkylated PAH derivatives (aPAHs), which are often more abundant and more toxic in real environmental matrices, are rarely included [6,23]. The grouping of all PAHs into a single class does not adequately reflect their actual toxicity, as it requires consideration of mechanisms of action and individual molecular properties, particularly for substituted derivatives [19, 31].

Conventional physicochemical soil remediation methods are often costly and may lead to secondary pollution. Therefore, increasing attention has been directed toward bioremediation, a process based on the use of microorganisms to transform contaminants into less toxic or harmless compounds [7]. Microorganisms capable of utilizing hydrocarbons as carbon and energy sources play a central role in these processes. The most studied genera include Pseudomonas, Mycobacterium, Rhodococcus, and Bacillus [27, 30].

The aim of this work is to analyze current approaches to the bioremediation of coal-contaminated soils, with a focus on the role of microorganisms in hydrocarbon degradation processes and an evaluation of the efficiency of various biotechnological methods.

2. Materials and Methods

This study was conducted as a review analysis. A systematic literature search was performed using international databases (Scopus, Web of Science, PubMed, ScienceDirect). Publications from 2015–2026 were included, with priority given to recent studies (2020–2026) focusing on soil bioremediation, PAH degradation, microbial consortia, and modern biotechnological approaches.

3. Results and Discussion

3.1 Composition of Coal-Related Contaminants and Their Environmental Impact

Literature analysis indicates that coal-related pollution consists of complex mixtures of organic and inorganic compounds, including PAHs, alkylated PAHs (aPAHs), phenols, resins, and heavy metals (Cd, Pb, Hg, As) [3]. Among them, PAHs are the most environmentally significant due to their high resistance to biodegradation and pronounced toxic effects.

PAHs are priority organic pollutants composed of multiple fused aromatic rings (e.g., naphthalene, anthracene, phenanthrene, pyrene). They are widely distributed in soil, water, and air and exhibit toxic, mutagenic, and carcinogenic effects on living organisms [28]. Their hydrophobicity, thermal stability, and ability to form stable complexes with other contaminants contribute to their long persistence in the environment [5,8].

High-molecular-weight PAHs (with four or more aromatic rings), such as benzo[a]pyrene, are particularly hazardous due to their carcinogenic and mutagenic properties [16]. Their strong affinity for soil organic matter reduces bioavailability but increases environmental persistence. In addition, alkylated PAH derivatives, which often dominate coal-derived wastes, may exhibit higher toxicity than their parent compounds, although their environmental risk is frequently underestimated [6, 35].

Thus, coal-related pollution represents a long-term source of complex ecological disturbance, affecting microbial communities, reducing soil fertility, and posing risks to human health.

3.2 Role of Microorganisms in Bioremediation

Numerous studies confirm that microorganisms are the key drivers of natural attenuation in contaminated soils. They are capable of utilizing hydrocarbons as carbon and energy sources, converting them into less toxic compounds [12].

Despite extreme conditions, coal-associated environments host diverse indigenous microbial communities with high functional potential, playing essential roles across all stages of the coal industry – from extraction to site reclamation [2]. The most active PAH-degrading microorganisms include species of Pseudomonas, Rhodococcus, Mycobacterium, Bacillus, and Sphingomonas [34]. These microorganisms possess specialized enzymatic systems (mono- and dioxygenases) that initiate the oxidation of stable aromatic structures [25].

Microbial consortia demonstrate particularly high efficiency, as different species complement each other’s metabolic pathways, enabling more complete mineralization of pollutants [4,9]. For example, one species may initiate PAH degradation, while another metabolizes intermediate products. The strain Acinetobacter sp. HAP1, isolated from refinery wastewater, efficiently degrades benzopyrene, and its association with cyanobacteria significantly enhances degradation efficiency [9]. Accordingly, microbial consortia and synthetic microbial communities represent more effective strategies than single strains [10].

Fungi, particularly white-rot fungi, also play an important role due to their extracellular enzymes (laccases, peroxidases) capable of degrading complex aromatic structures [21].

3.3 Mechanisms of Microbial Hydrocarbon Degradation

Biodegradation of coal-associated compounds by indigenous microorganisms (bacteria, fungi, and microalgae) is a promising approach for environmental restoration and industrial applications [2]. Coal, as a complex geopolymer, undergoes microbial transformation, and its properties and rank influence microbial community structure and functional potential.

Microbial degradation is a multi-step process involving initial activation, transformation, and complete mineralization to CO₂ and H₂O [24, 26]. The first step involves enzymatic oxidation of aromatic rings by dioxygenases, forming dihydrodiols, followed by ring cleavage via the catechol pathway and incorporation into central metabolic cycles (Krebs cycle) [17, 29].

For high-molecular-weight PAHs, low solubility limits degradation efficiency. Microorganisms overcome this through biosurfactant production and co-metabolism in the presence of additional carbon sources [14]. Anaerobic degradation occurs more slowly and involves alternative electron acceptors such as nitrates and sulfates.

Certain microbial groups (Gammaproteobacteria, Arthrobacter, Sinomonas, Bacillus) serve as bioindicators of PAH degradation and ecosystem status. Microbial activity is assessed using PLFA analysis, fatty acid profiling, and enzymatic assays, providing insights into ecosystem recovery [13,1].

3.4 Factors Influencing Bioremediation Efficiency

Bioremediation efficiency depends on both abiotic and biotic factors:

• Temperature: optimal range 20–35 °C; lower temperatures reduce degradation rates [11]
• pH: neutral to slightly alkaline conditions are most favorable [20];
• Aeration: essential for aerobic PAH degradation;
• Soil moisture: influences nutrient transport and microbial activity;
• Bioavailability: limited by sorption of PAHs to soil particles [18];
• Nutrient availability: nitrogen and phosphorus deficiency can significantly limit microbial growth [11,20].

Additionally, microbial community structure and the presence of adapted degraders are critical for effective remediation [2]. Biostimulation strategies involving nutrient addition (e.g., KNO₃, NaNO₃, NH₄NO₃, K₂HPO₄, MgNH₄PO₄) enhance microbial activity but may be limited by rapid nutrient depletion and soil characteristics [22].

Integrated approaches, including bioaugmentation and synthetic microbial consortia, as well as genetic engineering strategies, represent promising directions for improving degradation efficiency [36].

Conclusion

Coal-related pollution represents a complex and persistent mixture of toxic compounds, among which PAHs and their derivatives play a dominant role. Their high stability and toxicity necessitate effective remediation strategies. Microorganisms are the primary agents of bioremediation due to their ability to transform and mineralize hydrocarbons. The efficiency of these processes depends on both microbial metabolic capacity and environmental conditions.

Modern approaches, including biostimulation, bioaugmentation, and nanotechnology applications, significantly enhance degradation efficiency. A combined, integrated strategy tailored to site-specific conditions represents the most promising direction for future research and practical applications.

Acknowledgements

We acknowledge the Institute Microbiology of Academy Sciences of the Republic of Uzbekistan, which carried out a basic topic, for creating sufficient conditions to the experiments in the laboratory.

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